The present invention relates to a plasma processing apparatus that processes a substrate-like sample, such as a semiconductor wafer, arranged in a processing chamber disposed in a vacuum chamber using plasma formed in the processing chamber, and a method of operating the plasma processing apparatus, and in particular to a plasma processing apparatus that adjusts the sample processing using a result of detecting light from the processing chamber, and a method of operating the plasma processing apparatus.
In order to improve the performance of a semiconductor device, nanometer-level processing accuracy is required in a stage of processing a film structure having multiple film layers that include a mask layer and a film layer to be processed. The mask layer is preliminarily formed on a wafer surface to form circuits of the device on the surface of the substrate-like sample, such as a semiconductor wafer, by means of plasma etching. Furthermore, for the sake of improving the productivity of such a device, it is required to consecutively process wafers as many as possible while maintaining the accuracy in a wafer processing apparatus.
Unfortunately, such a consecutive operation of the stage in a mass production increases the time during which the inner walls of the processing chamber are exposed to plasma. The increase wears the inner wall itself, and deposits plasma-resistant compounds on the surface of the inner wall. Consequently, the state of the surface of the inner wall varies with the lapse of time. Such a variation in the material of the surface of the inner wall, in turn, varies the reactivity in plasma, the amount of disappearance of deposited radicals from the surface of the inner wall, and the amount of atoms and molecules released by reactions between the plasma and the material of the inner wall. The variations affect the plasma to vary the characteristics of this plasma accordingly.
These variations, in turn, vary the composition of the radicals and charged particles that constitute the plasma. If the variation resultantly varies the dimensions of the shape of the structure after processing to cause the amount of variation to exceed the permissible range, a semiconductor device obtained from the processed wafer becomes a defective piece, which reduces the production in yield. Consequently, the production cannot be continued. If the amount of deposition of such accretion on the surface of the inner wall increases, some of the accretion is separated from the surface, to which they have been accreted, to form shards and particles again toward the inside of the processing chamber. If the isolated substances are attached onto a surface of the wafer, the film structure is contaminated even through a process capable of achieving desired dimensions. The contamination reduces the production in yield as described above.
One of techniques of controlling the variation in processed shape described above is a technique that monitors the plasma state and apparatus state, feeds back the result of monitoring to adjust the plasma processing setting, and actively controls the processed shape (hereinafter, referred to as APC: Advanced Process Control). Among monitors for the plasma state, a spectroscopic (hereinafter, referred to as OES: Optical Emission Spectroscopy) monitor, which acquires a spectrum of plasma light, is adopted and applied to APC.
The plasma light is released when atoms or molecules having been excited by collision with electrons are de-excited in the plasma. Consequently, OES data reflects the amount and types of radicals, the electron number density, and the energy distribution in the plasma, thereby allowing the variation in plasma state to be obtained.
A processing chamber of a plasma apparatus for semiconductor processing is operated in a vacuum or reduced pressure atmosphere. Consequently, plasma light is obtained through the inner walls of the apparatus that allows the plasma light to pass, or a window or the like provided in the vacuum chamber walls. The plasma light obtained by OES is thus affected by the variation in the plasma light itself, and by reflection, scattering and the like caused in a process of the plasma light passing through the processing chamber wall.
Cases are assumed where even with different surface of the inner wall, the plasma states are controlled to be the same to thereby achieve the same processed shape. The plasma light before passing through the inner walls is the same between these cases. However, OES data obtained after the plasma light passes through the inner walls varies. Consequently, in order to achieve nanometer-level highly accurate APC, both the plasma light itself and variation in the inner surfaces are required to be obtained.
Conventionally, as these techniques, techniques disclosed in JP-A-2003-264175 and JP-A-H08-106992 have been known. For example, according to JP-A-2003-264175, light from an external light source (hereinafter, referred to as external light) is caused to be incident through a side of a processing chamber. A reflector provided on the surface of a side wall of the processing chamber on the opposite side is used to reflect the incident light.
This conventional technique corrects the OES data on the plasma light having passed through the surface of the inner wall using the OES data on the external light having passed through the inner wall, thereby obtaining the OES data on the plasma light before passing through the inner wall. According to JP-A-H08-106992, external light having entered from a side of a processing chamber is caused to pass through a side wall of the processing chamber on the opposite side to the outside. OES data on the external light having passed through the inner wall is used to obtain OES data on the plasma light before passing through the inner wall in a similar manner.
Furthermore, measures are taken according to which before start of a process of forming a circuit structure on a surface of a wafer, a coating step of forming a desired coating film on the surface of inner wall of the processing chamber is performed to stabilize the interaction between the inner surface of the processing chamber and plasma which is to be generated during wafer processing, thanks to presence of the coating film, thereby reducing variation in plasma characteristics and, in turn, temporal variation in processing results. Thus, such a conventional technique preliminarily forms the coating film so as to allow the film to last on the surface of the inner wall of the processing chamber from the start to the end of wafer processing, thereby reducing the variation in the state of the inner surface of the processing chamber.
As an example of such a conventional technique, a technique disclosed in JP-A-2002-246320 is also known. According to JP-A-2002-246320, in a state where products adhere onto a surface of metal of which inner walls of a processing chamber are made, the state of the film of accretion is detected using a result of detecting variation in the intensity of the interference light that includes reflected light from the surface of the inner wall made of the metal and from the surface of the film made of the accretion. This conventional technique discloses a technique that finishes cleaning so as not to expose the surface of the metal of which the inner walls of the processing chamber are made, on the basis of the detection result.